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proc: avoid information leaks to non-privileged processes

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By using the same test as is used for /proc/pid/maps and /proc/pid/smaps,
only allow processes that can ptrace() a given process to see information
that might be used to bypass address space layout randomization (ASLR).
These include eip, esp, wchan, and start_stack in /proc/pid/stat as well
as the non-symbolic output from /proc/pid/wchan.

ASLR can be bypassed by sampling eip as shown by the proof-of-concept
code at http://code.google.com/p/fuzzyaslr/ As part of a presentation
(http://www.cr0.org/paper/to-jt-linux-alsr-leak.pdf) esp and wchan were
also noted as possibly usable information leaks as well.  The
start_stack address also leaks potentially useful information.

Cc: Stable Team <stable@kernel.org>
Signed-off-by: Jake Edge <jake@lwn.net>
Acked-by: Arjan van de Ven <arjan@linux.intel.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jake Edge
2009-05-04 12:51:14 -06:00
committed by Linus Torvalds
parent 7fdf523067
commit f83ce3e6b0
2 changed files with 13 additions and 5 deletions
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5
fs/proc/base.c
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@@ -322,7 +322,10 @@ static int proc_pid_wchan(struct task_struct *task, char *buffer)
wchan = get_wchan(task);
if (lookup_symbol_name(wchan, symname) < 0)
return sprintf(buffer, "%lu", wchan);
if (!ptrace_may_access(task, PTRACE_MODE_READ))
return 0;
else
return sprintf(buffer, "%lu", wchan);
else
return sprintf(buffer, "%s", symname);
}